This is used when someone refuses to take responsibility for his or her own actions. It’s said with very little empathy and lots of sarcasm, so either you don’t like your friend so much or you already told him several times that he was making a mistake.

Questo detto invita alla prudenza, a non strafare e a non dire di poter fare o di avere una cosa, se ancora non è sicuro. (This saying invites one to be prudent, to not overdo it and not to say you can do or have something until it’s for sure.)